Download carboxylic acid

Chapter 10
Carboxylic Acids and Their Derivatives
Nomenclature
Physical properties
Acidity
Some reactions
Introduction
-carboxyl = carbonyl + hydroxyl
-acids around us: taste of vinegar,
sting (독아) of an ant (formic acid), rancid (악취나는)
smell of butter aspirin, ibuprofen(iso-butyl-propanoicphenolic acid), resilience (탄성) of polyester and
nylon fabric, Velcro (fabric hook-and-loop fasteners),
softness of silk, strength of bacterial cell wall
(N-acetylmuramic acid),our own membrane (fatty acids)
Aspirin
Ibuprofen
Nomenclature
-IUPAC system: “e” of alkane Æ -oic acid
-substituted acid
1)IUPAC: the chain is numbered beginning with carboxyl carbon
atom, and substituent (치환체) are located in usual way
2)common name: substituents are located with Greek letters,
beginning with α-carbon atom
e.g., 2-bromopropanoic acid (α-bromopropionic acid),
propenoic acid (acrylic acid),
3-hydroxybutanoic acid (β-hydroxybutyric acid)
-carboxyl group has priority over alcohol, aldehyde, ketone, and
prefix “oxo-” is used to locate carbonyl group of aldehyde and
ketone
e.g., 3-oxopropanoic acid, 2-bromo-4-oxopentanoic acid
Nomenclature
Pelagonium spp
(Geranium)
Nomenclature
-cyclic carboxylic acids: parent cycloalkane name + carboxylic
acid (e.g., cyclopentanecarboxylic acid, trans-3-chlorocyclobutanecarboxylic acid)
-aromatic acid: -oic or -ic acid
e.g., benzoic acid (benzenecarboxylic acid), p-chlorobenzoic
acid (4-chlorobenzenecarboxylic acid), o-toluic acid (2-methylbenzenecarboxylic acid), 2-naphthoic acid (2-naphthalenecarboxylic acid)
-aliphatic dicarboxylic acid: -dioic acid (IUPAC)
butanedioic acid, butynedioic acid, cis-2-butenedioic acid
(maleic acid), trans-2-butenedioic acid (fumaric acid)
-benzenedicarboxylic acids: phthalic acid, isophthalic acid,
terephthalic acid
-functional group: acyl, formyl, acetyl, propanoyl, benzoyl
Nomenclature
Sorrel (괭이밥)
Physical properties
-Colorless liquid with sharp (찌르는) or unpleasant (불쾌한) odor
e.g., acetic acid in vinegar, butyric acid-rancid butter, goat acids,
3-methyl-2-hexenoic acid-offensive (자극적인) odor from
armpit (겨드랑이)
-form H-bonding with themselves and with other molecules
Æ high bp (even higher than alcohol), e.g., glacial acetic acid
-form dimers by two
H-bonds
Acidity and acidity constant
-Carboxylic acids
dissociate in water,
yielding a carboxylate
anion and a hydronium
ion
(generally considered as
weak acids)
-Ka; acidity constant
What makes carboxylic acids acidic?
-More acidic for two reasons (compare dissociation of ethanol
and acetic acid, Fig 10-3, 4)
1)carbonyl carbon atom carries substantial (상당한) positive
charge Æmake it much easier to place a negative charge on
adjacent (인접한) oxygen atom
2)acetate ion is stabilized by resonance (see Fig in p292)
-In addition, C-O bond in ionized acids is shorter
(see Fig in P293)
Fig 10.1 compare acetate ion and ethoxide ion
Effect of structure on acidity
-Acidity can vary depending on what other groups are attached
to the molecule
-compare acidities of mono-, di-, trichloroacetic acids
(see the Fig in p293) Æ inductive effect
-recall (상기하다) that electron-withdrawing groups
enhance acidity and electron-releasing groups reduce
acidity
Preparation of acids
-Can be prepared in many ways
1) oxidation of primary alcohols or aldehydes (Fig 10.6)
2) oxidation of alkyl side chains on aromatic rings
(Fig 10.6 - 11)
3) reaction of Grignard reagents with carbon dioxide
(Fig 10.12)
4) hydrolysis of alkyl cyanide (Fig 10.13-14)
Carboxylic acid derivatives
-Compounds in which –OH of –COOH is replaced by various
other groups (e.g., ester, acyl halide, acid anhydride,
primary amides)
-many esters and amides occur naturally
Esters
-OH is replaced by –OR
-Named in a manner analogous (유사한) to carboxylic acid salt
i.e., the R part of –OR group is named first, followed by the
name of acid, with “–ic” ending changed to “–ate”
e.g., methyl acetate (methyl ethanoate), ethyl acetate (ethylethanoate), methyl butanoate
phenylacetate
methylbenzoate
Preparation of esters: mechanism, nucleophilic
Acyl substitution
-carboxylic acid react with alcohol in the presence of acid
catalyst to form ester (Fischer esterification)
-Mechanism (6 steps, see Fig 10-19)
1) protonation of carboxyl group
2) alcohol, as a nucleophile, attacks carbonyl carbon of
protonated acid
3), 4) equlibria on oxygen between proton loss and gain
5) water formation (as a leaving group)
6) deprotonation and ester formation
Lactones
-lactones: cyclic ester, can be formed from hydroxy acids
(HO-R-COOH), mostly five or six-membered rings
-lactone compunds around us: coumarin (newly mown hay),
nepetalactone (catnip), erithromycin (antibiotics, a macrocyclic lactone) (p303)
Coumarin
Nepetalactone
Penicillin
catnip